Bats: Researchers ‘See’ in Echolocation for the First Time

Anyone familiar with bats knows that the term “blind as a bad” actually translates to “not blind at all.” Not only do these animals have perfectly functioning eyes, but they also have the help of sonar in failing light. Now researchers have found a way to show what bats “see” with that echolocation, and the results have revealed some impressive findings.

“Using information like X-rays to build pictures is well established in medicine with the use of CT scans and ultrasound, but no-one has ever before attempted to create images from sounds generated in ecology,” lead researcher Elizabeth Clare, from the Queen Mary University of London (QMUL), explained in a statement.

“We constructed a brand new technique for tomographic imaging which allows us to perceive more accurately which cues are most important to the bat,” added study co-author Marc Holderied, from the University of Bristol.

Clare and Holderied were specifically interested in a distinction in the way bats hunt. Researchers have long known that many bat species (but not all) use echolocation almost as a homing mechanism, allowing them to swiftly close in one even the most agile of prey. However, researcher have also theorized that bats also used use sonar to detect prey that would likely remain undetected by the naked eye, especially in the evening.

(Photo : Clare et al. eLife, 2015) Moths were placed on one of four common surfaces (A) bark, (B) leaf, (C) limestone, and (D) slate. The researchers then generated acoustic tomographies with and without the specimen (left and right in panels E–H, respectively).

The results of their work, which was recently published in the journal eLife, provides a better understanding of this second hunting strategy. Specifically, the researchers confirmed that bats use their regular sonic ‘surveys’ of an area from multiple angles, along with their memory of past sweeps, to investigate if anything is out of place.

It’s possible that bats remember the layout of their hunting grounds down to the surface of individual leaves and stones. When one of these familiar leaves is covered by an insect, the normal echoes are interrupted and the winged hunters are cued to swoop in.

For their work, Clare and Holderied chose to look at the common big-eared bat (Micronycteris microtis), a neotropical species from South and Central America, as these bats are known to nearly exclusively rely on echolocation (as opposed to smell or sight) for late-night hunts. (Scroll to read on…)

(Photo : Calre et al. eLife, 2015) The image of a sonic echo bouncing off slate with and without prey sitting atop it.

Interestingly, the shape of an insect didn’t seem to matter in a hunt. While a predator relying on its eyes may zero in on an insect with protruding wings and sharp angles, M. microtis was just as proficient at nabbing insects laying low as it was with insects that stick out. What’s more, the bat proved most proficient at finding insects on leaves or still water.

“Our findings suggest a new phenomenon of acoustic camouflage,” added Clare, “where insects are harder to discern on rough surfaces such as bark, and bats compensate for this by focusing their attention on the simpler, mirror-like surfaces in their patch.”